The production of containers of thermoplastic material, such as bottles, jars, etc., is generally carried out from preforms, sometimes called blanks, which are introduced into a molding device with which forming means are associated, for example blow-molding or stretch-blow-molding means.
In the following description and in the claims, the preforms and the finished containers will be designated under the generic term “hollow bodies.” Traditionally, in this technical field, the preform and the finished container have an identical neck or throat. Consequently, the same element for support of a preform by its neck is also suited to support a finished container.
The installation for producing containers is supplied with preforms that are not in a state to be directly formed because of their insufficient temperature. Prior to their molding by blow molding or stretch blow molding, the preforms are therefore heated in a heating station so as to impart to them a sufficiently malleable structure for the blow-molding operation.
Such mass-production installations for containers are equipped with a heating station comprising a heating tunnel equipped with means for heating the preforms. This heating tunnel determines a heating path along which the preforms are generally transported by a conveyor at a stabilized speed without stopping. The tunnel has sufficient length to make possible the heating of the preforms during their transit.
The conveyor comprises individual support elements for the preforms that move along a closed circuit, a portion of which transports the preforms along the heating path that passes through the heating tunnel. The support elements are generally formed by mandrels that are able to drive the transported preforms in rotation around their axis to guarantee a homogeneous heating of the preforms.
Furthermore, the preforms are brought one after the other by an input device to an input zone in the heating station. The input device is generally formed by a rotating wheel equipped on its periphery with support elements for the preforms, such as notches or clips. The preforms are thus loaded on the conveyor in the area of the input zone, in which the path of the support elements of the conveyor is tangential to the path of the support elements of preforms of the input device.
To make possible a transfer of the preforms from the input device to the conveyor, the support elements of the conveyor must travel in a coordinated way, both in position and in speed, with the support elements of the input device in the input zone. On the input wheel, the preforms are spaced by a spacing that is determined according to their direction of movement. Consequently, it is absolutely essential that the individual support elements of the conveyor be spaced with a separation that is equal to the input spacing of the preforms during their passage in the input zone.
The same problem is encountered for the transfer of the hot preforms, at the output of the heating path, to an output device that is similar to the input device.
Furthermore, the heating station comprises a particularly long and cumbersome heating tunnel. It would therefore be advantageous to be able to make a shorter, and therefore more compact, heating tunnel without thereby degrading the quality of heating of the preforms.
In addition, in the heating stations that are known from the state of the art, the preforms moving in the heating tunnel are separated from one another by a relatively large spacing. Consequently, a large portion of the heating radiation emitted by the heating means is produced to no purpose, because it goes through the spaces left between two successive preforms without heating the latter. Thus, a large amount of energy is squandered.
According to another problem, the hot preforms are intended to supply at least one subsequent treatment station, in particular the forming station. It frequently happens that the spacing between two successive preforms in the subsequent treatment station is different from the spacing between two successive preforms transported by the input device. Consequently, a transfer device that is able to change the spacing between two preforms is generally inserted in the flow of the preforms downstream from the furnace and upstream from said subsequent treatment station.
Such a transfer device with change of spacing is not only expensive, but it also has the drawback of increasing the dimensions of the forming installation.